Quantum cascade lasers (QCL) are semiconductor lasers providing light in the mid- and far-infrared wavelength ranges. QCLs generally involve intersubband transitions in the conduction energy band, which, in turn, leads the generated light to be transverse-magnetic (TM) polarized. Quantum cascade lasers have been made utilizing first-order distributed feedback gratings (DFB). Although first-order DFB QCLs can provide desirable single-mode emission, the lasers are edge-emitting, i.e., laser light is emitted from a cleaved facet. Surface or substrate emission has been achieved using QCLs utilizing second-order distributed feedback gratings, thereby eliminating the need for cleaved facets to emit the light. However, second-order DFB QCLs have generally operated in an antisymmetric longitudinal mode, resulting in a double-lobe, far-field beam pattern. In order to achieve a single-lobe, far-field beam pattern, the second-order DFB gratings may include a π phase shift. Nevertheless, even with a π phase shift, the internal lasing mode of the second-order DFBs QCLs remains antisymmetric longitudinally which, in turn, causes a decrease in efficiency with increasing device cavity length, and low potential for continuous-wave (CW) operation at high output powers.